Heat-hardenable binders for coating compositions



United States Patent 3,532,769 HEAT-HARDENABLE BINDERS FOR COATINGCOMPOSITION S Horst Dalibor and Hans-Joachim Kiesslmg, Hamburg, Germany,assignors to Reichhold Chemicals, Inc.,

White Plains NY. No Drawing. Filed Mar. 10, 1967, Ser. No. 622,080Claims priority, application Germany, Mar. 28, 1966,

Int. Cl. C08f 36; C08g 37/32 US. Cl. 260-855 13 Claims ABSTRACT OF THEDISCLOSURE The present invention relates to heat-hardenable bindershaving as a basis mixtures consisting of etherified ammoplasts andreaction products of copolymers and polyols that are soluble in organicsolvents, the copolymers being prepared from 0:,B-UI1S8tLlI3tflddicarboxylic acid anhydrides, aromatic vinyl compounds, methacrylic acldesters, acrylic acid esters and/or fumaric acid esters. Moreparticularly, the binders according to the present invention contain (a)50 to 95% by weight of soluble reaction products of copolymers whichhave been prepared by heating at reaction temperatures, preferably lessthan mole percent and not more than percent of n p-unsaturateddicarboxylic acid anhydride and styrene, vinyltoluene, vinylxylene ornuclear-halogenated styrenes, methacrylic acid esters, acrylic acidester and/ or fumaric acid ester, with trito hexavalent alcohols, ifnecessary together with monoor dialcohols, to an acid number of 5 to 60,preferably 20 to 50, and a hydroxyl number of 20 to 120, preferably to90, and (b) 5 to 50% by weight of ureaor aminotriazine-formaldehyderesins etherified with alcohols.

RELATED APPLICATIONS The present application is related to thefollowing: (1) US. application Ser. No. 622,039, filed Mar. 10, 1967,corresponding to German application R 42,945, filed Mar. 28, 1966(2054); (2) US. application Ser. No. 622,112, filed Mar. 10, 1967,corresponding to German application R 42,946, filed Mar. 28, 1966(2055); (3) US. application Ser. No. 622,090, filed Mar. 10, 1967, nowPat. No. 3,474,076, granted Oct. 21, 1969, Corresponding to Germanapplication R 42,947, filed Mar. 28, 1966 (2056); and (4) U8.application Ser. No. 622,041, filed Mar. 10, 1967, corresponding toGerman application R 42,948, filed Mar. 28, 1966 (2057).

Heat-hardenable binders for coating compositions consisting ofaminotriazine formaldehyde resins and plasticizing components havinghydroxyl and carboxyl groups are known. As the plasticizing component itwas customary to use therewith condensation resins of low molecularweight or high molecular weight polymers having thermoplasticproperties.

German Pat. 544,326 describes the preparation of anhydridegroups-containing polymers reacted with monoand polyols. However,soluble anhydride groups-containing polymers reacted with monoordialcohols are unimportant as binders for coating compositions,particularly for lacquer raw materials, since even combinations thereofwith ureaor aminotriazine-formaldehyde resins resulted in coatingshaving insufficient resistance to solvents, Water and bases. Solubleanhydride groups-containing copolymers of the kind reacted only withtriols could not, however, be obtained by the process of German Pat.544,326.

Copolymers, as described in the examples of the aforesaid German patent,having a content of 30 and more percent by weight of maleic acidanhydride in the copolymer, yield insoluble products upon being reactedsolely with trivalent alcohols, before achieving compatibility withureaor aminotriazine-formaldehyde resins.

It has now been found that it is possible to obtain products that aresuitable for coating compositions if the component (a) contains reactionproducts of polyols and copolymers that have preferably at least 1% andpreferably less than 20 mole percent by weight of afiunsaturateddicarboxylic acid anhydride and not more than 25% by weight, andcomponent (b) is in the form of aminotriazine-formaldehyde resins.Suitable as component (a) are reaction products of copolymers andpolyols such as trito hexavalent alcohols, if necessary together withmonoand dialcohols.

Moreover, it was found that reaction products (a), particularly suitablefor use in combination With etherified aminotriazine-formaldehyde resinsas binders for coating compositions, are those wherein the copolymersare reacted with trivalent alcohols, without the use of monoand divalentalcohols. Outstanding properties were found in the case of reactionproducts (a) wherein the polyols are trivalent alcohols and, moreparticularly, those that are less polar then glycerin, as for examplehexanetriol 1,2,6 or trimethylolalkane. Of the latter, the most suitablefor the preparation of the reaction products (a), that constitute thecomponents of the combinations used in accordance with the presentinvention, are those wherein for each mole of anhydride in the copolymerthere are used 0.8 to 1.5 mole, preferably 0.8 to 1.2 mole oftrimethylol-propane.

By the partial reaction for the preparation of component (a) fromcopolymers having a content of at least 1 but preferably less than 25mole percent, preferably of 5 to 10 mole percent of an a s-unsaturateddicarboxylic acid anhydride, with polyols of the aforesaid type, it ispossible to obtain soluble reaction products which, aside from an acidnumber of 5 to 60, preferably of 20 to 50, possess an hydroxyl number of20 to 120, preferably of 30 to 90.

For the heat-hardenable coating compositions according to the presentinvention, the content of free hydroxyl groups possessed by thecomponent (a) is a prerequisite for the combination and compatibilitywith aminoplast resins particularly the aminotriazine-formaldehyderesins, and for the cross-linking reactions with the methylolormethylolether groups, which take place upon heating and which arepromoted by the free carboxyl groups.

In the copolymers to be reacted with triols, it is possible to useinstead of maleic acid anhydride other afiunsaturated dicarboxylic acidanhydrides, such as itaconic acid anhydride. When maleic anhydride isused it should be less than 20% by Weight and when itaconic acid isemployed it should be not greater than 25% by weight.

For the use as binders in coating formulations in accordance with thepresent invention, the structure as well as the composition of thestarting polymers that serve to prepare the component (a) is ofconsiderable importance. Aside from 04,,[3-1111S8tl1lfll6d dicarboxylicacid anhydrides, the following monomers can be used for the preparationof the copolymers: styrene, vinyltoluene, acrylic acid esters,methacrylic acid esters and fumaric acid esters, each having 1 to 10carbon atoms in the alcohol component thereof. The selection of thecomonomcr mixture depends upon the particular use contemplated for thecopolymer reacted with polyols as binders for coating compositions and,based upon the nature of the rigid or flexible surfaces to be coated,must generally conform to the desired properties such as hardness andelasticity.

Monomers that impart hardness properties to the starting polymers arefor example aromatic vinyl hydrocarbons, such as styrcnes andnuclear-halogenated styrenes as well as methacrylate. Acrylic acidesters having two or more carbon atoms in the alcohol portion thereof,methacrylic and fumaric acid esters with four and more carbon atoms inthe alcohol portion thereof, when used as comonomers, generally producesoftness and flexibility in the copolymer if the alcohol portion inthese monomers is not branched.

The copolymers serving as a basis for the present novel coatingcompositions are prepared in known manner at raised temperatures,preferably in aromatic solvents, for example in xylene or high-boilingmixture of aromatics. The reaction takes place in a temperature rangebetween 50 and 250 C. preferably from 90 to 170 C., by a freeradical-polymerization process. This process is carried out in thepresence of catalysts yielding free radicals such as peroxides, as forexample benzoyl peroxide, di-tert.-butylperoxide or azo compounds.However, the reaction can also be carried out thermally at highertemperatures. When using low-boiling copolymerizable monomers, ormonomers that are gaseous at room temperature, it is necessary tooperate under pressure. In carrying out the process according to thepresent invention, it is generally preferred to effect the reaction withthe polyols in a solvent that is the same as the solvent used for thepolymerization of the monomers. In addition to the preferred aromaticsolvents used, it is possible to operate in the presence of othersolvents which do not participate, or only participate to a smallextent, in the esterification reaction, as for example, aliphatichydrocarbons, ketones, esters and tertiary alcohols.

The viscosities of the solutions of the starting polymers, measured in60% solutions at C. on the Gardner- Holdt scale, may lie within thewhole range of this scale. Products having Gardner viscosities from A toD should be classified as copolymers of low molecular weight,

those having viscosities from E to Y copolymers of average molecularweight, and those with viscosities from Y to Z copolymers of highmolecular weight.

Since the reaction between the copolymers, in a solution of aromatics,and the polyols requires at higher temperatures relatively long periods,the content of free hydroxyl groups gives rise, possibly as sidereactions, to reesterifications between these and the ester groups thatare brought into the copolymer, for example, by the use of acrylic acidor methacrylic acid alkylesters, or fumaric acid dialkylesters.Methacrylic acid esters have less tendency to undergo reesterificationthan acrylic acid and fumaric acid esters. The extent of thereesteri-fication also depends upon the nature of the alcohol that iscombined in the monomers in the form of esters. Methanol is split offmore readily than ethanol, and so on. Ester groups with secondary ortertiary alcohols show only slight or no tendency towardreesterification. These reesterification reactions are of importance inthe selection of the copolymer for the reaction with trivalent alcohols.The copolymers having high molecular weights should not contain groupsthat are inclined to reesterify since this would produce, in the courseof the triol reaction, a certain amount of gel formation due tocross-linking, before achieving compatibility with the melamine resins.The reesterifications must, therefore, be confined to limits above whichit is not possible to avoid the formation of insoluble or gel likereaction products due to cross-linking, before achieving compatibilitywith the melamine resins.

In general, it is possible to achieve the desired hardness through theinclusion of copolymerized styrene or methylmethacrylate and theflexibility through the inclusion of copolymerized acrylic and/orfumaric acid esters wherein the carbon chain in the alcohol componentcontains more than four carbon atoms.

The alkylated aminoplasts contained in the heat-hardenable binder of thepresent invention as component (b) thereof in accordance with thepresent invention are prepared by alkylation of a condensation productobtained from an aldehyde and urea, N,N-ethyleneura, dicyandiamide oraminotriazines, by means of an alkanol containing 1 to 6 carb on atoms.It is possible to use an alkylated aminoplast on condition that it issoluble that it is soluble in the organic solvent used for thepreparation of the coating composition. In general, the alkylatedaminoplast should contain at least and preferably 100% methylol group,which are alkylated with an al'kanol having 1 to 6 carbon atoms. It ispreferred to use alkylation products that were obtained with alkanolshaving 3 to 6 carbon atoms. The butylated products are particularlydesirable because of their greater compatibility with a large number ofpolyol reaction products and solvents.

Aminotriazines contained in component b suitable for the preparation ofthe aminoplast are: melamine, acetoguanamine, benzoguanamine,formoguanamine, ammeline, 2-chloro 4,6 diamino-1,3,5-triazine,2-phenylp-hydroxy-4,6 diamino 1,3,5-triazine, 6-methyl-2,4-diamino-1,3,5triazine, 2,4,6 trihydrazine-1,3,5-triazine, 2,4,6triethyl-triamino-1,3,5-triazine or N,N-di-(C -C alkylmelamine, such asN,N-dimethylmelarnine. As the aldehyde, although most aldehydes aresuitable, such as acetaldehyde, crotonaldehyde and acrolein, it ispreferred to use condensation products prepared with reversible polymersof formaldehyde, such as paraformaldehyde.

The copolymers reacted with the polyols constituting component (a) andthe aminoplasts constituting component (b) are dissolved in an organicsolvent in a ratio of 50 to parts of copolymer to 50 to 5 parts ofaminoplast. The quantitative relations of component (a) and alkylatedaminoplast must be chosen in such a way that the two components arecompatible in the coating solution as well as in the finished film. Itis possible to use any desired concentration of the copolymer ascomponent (a) and of the aminoplast as component (b) in the solvent, forexample, from 1 to 60% by weight. If a pigment is present, the totalcontent of the solids in the coating composition should lie between 5and 75% by weight. The ratio of pigment to binder, i.e., component (a)plus component (b), can lie between 1:20 and 20:1.

As solvents it is possible to use: hydrocarbons, such as benzene,toluene, xylene and aromatic naphthenes or mixtures of such solvents;esters, such as ethyl, butyl, amyl, ethoxyethyl or methoxyethyl acetate,lactate or propionate; ketones, such as acetone, methylisopropylketonemethylisobutylketone, dioxane, isophoronehexanone or cyclohexanone;alcohols, such as n-butanol, t-butanol, isopropyl alcohol, n-propylalcohol, amyl alcohol and cyclohexanol: ethers, such as diethylether,the monoethyl, monomethyl and monobutylether of ethylenglycol andvarious other solvents, such as dimethylformamide, dimethylacetamide,acetonitrile, nitromethane, nitroethene, nitropropane or nitrobutane, aswell as mixtures of two or more solvents belonging to the same group aswell as of several or all of the groups mentioned above.

As pigments it is possible to incorporate: inorganic pigments, such aschrome yellow, Prussian blue, Brunswick green; titanium pigments, suchas titanium dioxide, extended titanium pigments (which are extendedeither with precipitated or natural fillers, such as alkaline-earthmetal sulfates, as for example, calcium sulfate and barium sulfate);toned titanium pigments, titanates, such as barium, zinc, lead andmagnesium titanate. Also other types of inorganic pigments can be used,for .example, zine sulfide pigments, such as zinc sulfide, lithopone,extended zinc sulfide pigments, such as lithopone with a calcium basis,zinc sulfide, zinc oxide or antimony oxide extended with naturalfillers; or organic pigments, i.e., organic dyes that are free ofsulphonic or carboxylic acid groups or other groups that impartwater-solubility. The expression pigment also embraces otherWaterinsoluble organic dyes, as for example, the calcium or bariumlacquers of azo lacquer dyes.

The new coating compositions can be applied to the substrate in anydesired fashion, for example, by brushmg, spraying, dipping or rollingon. They are then dried and hardened by heating. In general, it is notnecessary to add curing catalysts. However, an acid catalyst can beadded, if necessary. The amount of such a catalyst may lie between 0.1and 1% by weight based upon the weight of the aminoplast. The use of acuring catalyst may be appropriate when it becomes necessary to applylow hardening temperatures. When curing catalysts are used, it ispossible to achieve insolubility simply by drying and aging at roomtemperature. The catalysts used for the hardening treatment to set upthe compositions according to the present invention, can be any acidcatalyst, including all organic and inorganic acid catalysts. Forexample, it is possible to use a catalytic amount of sulfuric orhydrochloric acid or the salts thereof, as for example, ammonium sulfateor ammonium chloride, or an organic acid, such as acetic acid, phthalicacid, benzoic acid, toluene sulfonic acid, naphthalenesulfonic acid orthe monosalt of maelic acid with triethylamine.

The drying of the coatings can be eifected at raised temperatures, forexample, 60 to 104 C. The hardening can be carried out at 80 to 230 C.,whether or not a catalyst is present. The hardening period may lie inthe upper temperature range of about 230 C. between /2 and 2 minutes andin the lower temperature range of about 80 C. between 1 and 2 hours.However, it is particularly advantageous to elfect the hardening for 15to 30 minutes at 120 to 130 C.

EXAMPLE 1 (A) Preparation of component (a) contained in the coatingcomposition.24 parts by weight of laurylmercaptan and 944 parts byweight of an aromatic solvent mixture having boiling ranges from 150 to170 C. are introduced into a three-necked flask equipped with a stirrer,thermometer and reflux cooler, and heated to 130 to 140 C. A mixtureconsisting of 16 parts by weight of di-tert.-butyl peroxide, 280 partsby weight of styrene, 420 parts by weight of methylmethacrylate, 106parts by weight of maleic acid anhydride and 590 parts by weight ofZ-ethylhexylacrylate, is then added within a period of 2 hours andpolymerized for an additional 4 hours. The body content of the solutionamounts to 61% and the viscosity corresponds to that of X and Y on theGardner-Holdt scale. The resin solution is clear at room temperature.

The resin is incompatible with melamine-formaldehyde resins, even afterbeing baked (ratio 70:30). 1000 parts by weight of the 61% resinsolution are mixed with 62 parts by weight of trimethylolpropane andheated under reflux at about 168 to 172 C. After a reaction period of 6hours, the reaction product was found to be compatible withmelamine-formaldehyde resins after being baked. The product is nowdiluted with isobutanol to a body content of 50%. The viscosity of the50% solution was approximately that of U on the Gardner-Holdt scale,whereas the acid number was 35 and the hydroxyl number about 75.

(B) Preparation of the heat-hardenable coating composition totaling upto 70% of copolymer to 30% of melamine resin.-700 parts by weight of thereaction product according to Example 1A were mixed at room temperaturewith 300 parts by weight of an isobutanol etherifiedmelamine-formaldehyde resin constituting component (b) prepared inaccordance with German Pat. No. 1,127,083.

The melamine resin used was prepared by the process described in Example1 of German Pat. 1,127,093 in such a way that, after the separation ofwater, it had a viscosity of A-B on the Gardner-Holdt scale, the excessisobutanol being then distilled oif and replaced with xylene until thesolution had a solids content of 50 to 52% by weight and a viscosity of50 to 70 DIN-seconds at 20 C.

This mixture consisting of reaction product (a) and the melamine resinsolution and 340 grams of TiO (rutile) was made into a lacquer bygrinding which was diluted with butyl-acetacte to a spraying viscosityof 20 DIN-seconds. It was applied to phosphated sheet metal and bakedfor 30 minutes at C. The film had an excellent gloss, great flexibility,good surface hardness as well as a good resistance to xylene.

EXAMPLE 2 (A) Preparation of component (a) contained in the coatingcomposition.In the same way as explained in Example 1A, 24 parts byWeight of lauryl mercaptan, 944 parts by weight of a mixture of aromaticsolvents having boiling ranges of 150 to 170 C., are heated to 130 toC., whereupon a mixture consisting of 16 parts by weightdi-tert.-butylperoxide, 560 parts by weight of styrene, 140 parts byweight of methylmethacrylate, 106 parts by weight of maleic acidanhydride and 590 parts by weight of Z-ethylhexylacrylate is addedwithin a period of 4 hours and polymerized for an additional 2 hours.

The body content of the solution amounts to 60% and the viscositycorresponds to that of W to X on the Gardner-Holdt scale. The resinsolution is clear at room temperature.

The resin is incompatible with melamine-formaldehyde resins, even afterbeing baked (ratio 70:30).

1000 parts by weight of the 60% resin solution are mixed with 62 partsby Weight of trimethylol-propane and are heated under reflux to about168 to 172 C. After a reaction period of 7 hours, the reaction productwas found to be compatible with melamine-formaldehyde resins after beingbaked. The product is now diluted with isobutanol to a body content of50%. The viscosity of the 50% solution was approximately that of W to Xon the Gardner-Holdt scale, whereas the acid number was 37 and thehydroxyl number about 65.

(B) Preparation of the coating composition totaling up to 66.6% ofreaction product according to Example 2A to 33.3% melamine resin.-666grams of the reaction product prepared according to Example 2A, 333grams of the 50% solution of isobutanol-etherified melamineformaldehyderesin described in Example 1 and 340 grams of Ti0 (rutile) are made intoa lacquer by grinding, which is then diluted with butylacetate to aspraying viscosity of 20 DIN-seconds. It was applied to phosphated sheetmetal and baked thereon for 30 minutes at 140 C. The film obtained inthis manner, upon being treated for 10 hours at 90 C. with a 1% alkalinealkylarylsulfonate washing liquer, did not show a decrease of gloss orthe formation of blisters.

EXAMPLE 3 (A) Preparation of component (a) contained in the coatingcomposition-In the same Way as explained in Example 1A, 24 parts byweight of laurylmercaptan, 944 parts by weight of a mixture of aromaticsolvents having boiling ranges of to 170 C., are heated to 150 to 170C., whereupon a mixture consisting of 16 parts by weight ofdi-tert.-butylper-oxide, 280 parts by weight of styrene, 350 parts byweight of methylmethacrylate, 106 parts by Weight of maleic acidanhydride and 670 parts by weight of butylacrylate is added within aperiod of 4 hours and polymerized for another 2 hours.

The body content of the solution amounts to 60% and the viscositycorresponds to that of V to W on the Gardner-Holdt scale. The resinsolution is clear at room temperature.

The resin is incompatible with melamine-formaldehyde resins, even afterbeing baked (ratio 70:30).

1000 parts by weight of the 60% resin solution are mixed with 62 partsby weight of trimethylol-propane and are heated under reflux to about168 to 172 C. After a reaction period of 8 hours, the reaction productwas found to be compatible with melamine-formaldehyde resins after beingbaked. The product is now diluted with 7 isobutanol to a body content of50%. The viscosity of the 50% solution was approximately that of U to Von the Gardner-Holdt scale, whereas the acid number was 36 and thehydroxyl number about 75.

(B) Preparation of the coating composition totaling up to 70% ofcomponent (a) to 30% of melamine resin.700 grams of the reaction productprepared according to Example 3A, 300 grams of the 50% solution ofisobutanol-etheified melamine-formaldehyde resin described in Example 1,constituting component (b), and 340 grams of Ti (rutile) are made into alacquer by grinding which is then diluted With butyl acetate to aspraying viscosity of 20 DIN-seconds. After applying it to phosphatedsheet metal it was baked theren for 30 minutes at 130 C. The filmobtained in this manner,

upon being treated for 1 hour with xylene did not show I diminishedgloss.

It is preferred to use as components for the binder according to thepresent invention, reaction products of copolymers and trito hexavalentalcohols where the copolymerized acrylic acid ester and/or fumaric acidester are those that were copolymerized in the form of monomers such asdibutylfumarate, di-Z-ethylhexylfumarate, bnutylacrylate and2-ethylhexylacrylate.

We claim:

1. A binder suitable for forming heat-hardenable coating compositionssoluble in organic solvents, comprising a blend of (A) 50 to 95% byweight of a soluble reaction product of the following reaction (1) acopolymer prepared by heating at reaction temperature the followingingredients (a) 125% by weight of an 0:,[3-111188111- rated dicarboxylicacid anhydride and (b) at least one monomer of a group consisting ofstyrene, vinyltoluene, vinylxylene and nuclear-halogenated styrenes, and(c) at least one alkyl esters selected from a group consisting ofalkylmethacrylate, alkylacrylate and dialkylfumarate, wherein the alkylradical contains from 1 to 10 carbon atoms with (2) a trihydric alcohol,until an acid number of 5 to 60, and an hydroxyl number of to 120 isobtained, and (B) 5 to 50% by weight of an aminoplast selected from agroup consisting of urea-formaldehyde and aminotriazine-formaldehyderesins etherified with alcohols.

2. A binder according to claim 1 wherein (2) includes in addition to thetrihydric alcohol, at least one member of a group consisting of mono anddialcohols.

3. A binder according to claim 1 wherein component (A) has an acidnumber of 20-50.

4. A binder according to claim 1 wherein component (A) has an hydroxylnumber of -90.

S- A binder according to claim 1 wherein ingredient (a) comprises maleicanhydride.

6. A binder according to claim 1 wherein ingredient (a) comprises 510%by weight of maleic anhydride.

7. A binder according to claim 1 wherein ingredient (a) comprisesitaconic acid anhydride.

8. A binder according to claim 1 wherein ingredient (a) comprises 6-12%by weight of itaconic acid anhydride.

9. A binder according to claim 1 wherein the proportion of the reactantsin (2) is from .81.8 moles of alcohol per mole of the anhydride reactant(1).

10. A binder according to claim 9 wherein the proportion of reactants isfrom .8-1.2 moles of alcohol per mole of the anhydride reactant (1).

11. A binder according to claim 1 wherein reactant (2) is selected froma group consisting of trimethylol propane, trimethylolethane andheXanetriol-1,2,6 and mixtures thereof.

12. A binder according to claim 1 wherein component (B) comprises amelamine formaldehyde resin etherified with butanol.

13. A binder according to claim 1 which is characterized in that ascomponent (A) it contains reaction products obtained from 5 to 10% byweight of maleic acid anhydride and from monomers selected from thegroup consisting of 10% to 50% by weight of styrene, 0 to 50% by weightof alkylmethacrylate, 10% to by weight of alkylacrylate, 10% to 85%dialkylfumarate, wherein the alkyl radicals contain from 1-10 carbonatoms.

References Cited UNITED STATES PATENTS JOHN c. BLEUTGE, Primary Examiner

